var ifclick = false,
    start_x,
    change_x;
$('.rotary').mousedown(function(e){
  ifclick = true
  start_x = e.pageX
})
$('.rotary').mouseover(function(e){
  if(ifclick){
    change_x = e.pageX - start_x
    if(change_x > 0){
      go_left(change_x)
    }
  }
})
$('.rotary').mouseup(function(){
  ifclick = false
})

function go_left(sum){
  
}